Single -core fiber has a core diameter of ______ microns.

Single -core fiber has a core diameter of ______ microns.

• A. 7
• B. 8
• C. 10
• D. 9

Answer: (D)

Single-mode fiber is designed to carry light in a single transverse path, which requires a very small core so that only the fundamental mode can propagate at common telecom wavelengths. The standard nominal core diameter that achieves this is about 9 micrometers. Keeping the core around this size ensures the V-number stays below the cutoff for higher-order modes, minimizing modal dispersion and allowing longer link distances. Smaller values, like 7 or 8 micrometers, would be outside the typical standard and can complicate manufacturing and performance consistency. A larger core, such as 10 micrometers, pushes the fiber toward supporting more than one mode at those wavelengths, depending on the numerical aperture and operating wavelength. Hence, 9 micrometers is the best match for a single-mode fiber core diameter.

Single-mode fiber is designed to carry light in a single transverse path, which requires a very small core so that only the fundamental mode can propagate at common telecom wavelengths. The standard nominal core diameter that achieves this is about 9 micrometers. Keeping the core around this size ensures the V-number stays below the cutoff for higher-order modes, minimizing modal dispersion and allowing longer link distances.

Smaller values, like 7 or 8 micrometers, would be outside the typical standard and can complicate manufacturing and performance consistency. A larger core, such as 10 micrometers, pushes the fiber toward supporting more than one mode at those wavelengths, depending on the numerical aperture and operating wavelength. Hence, 9 micrometers is the best match for a single-mode fiber core diameter.